Elastic heater for compound curves



Oct. 6, 1964 n. R. BARBOUR ETAL 3,152,313

ELASTIC HEATER FOR COMPOUND CURVES Filed NOV. 28, 1958 vi I y t m w Z 9nBC A 3,152,313 ELASTIC HEATER FOR COMPOUND CURVES Donald R. Barbour,Coxsackie, and Robert V. Cahlll, Catskill, N.Y., assignors to GeneralElectric Company, a corporation of New York Filed Nov. 28, 1958, Ser.No. 777,101 1 Claim. (Cl. 338-214) This invention relates to an elasticheater to be used for compound curves and, more particularly, to aninsulated heater device constructed so that it has elasticity in alldirections to thereby conform to the compound curvature of a surface.

In many present day installations requiring the use of heaters, such asheaters used to temperature cure aircraft bonded structures and thelike, some of the surfaces to which the heat is to be applied arecomposed of a variety of simple and compound curves. In those instancesin which the heat must be applied to a compound curvature it isgenerally necessary to tailor that portion of the heating device tospecifically conform to such compound curve. As will be readilyapparent, this special tailoring of a portion of the heating devicenecessarily increases the cost of the heater, while at the same timerendering the heating device relatively ineffective for otherinstallations. Also, due to the special tailoring of such heatingdevices, any change which may later be made in the compound curve forwhich the heating device was specifically designed, will cause theheating device to be less effective in such installation, if notcompletely useless therefor.

There are presently available today heating devices which are flexibleand can thereby adjust to simple curves, but such heating devices do nothave the necessary elasticity to conform to compound curves. That is,these heating devices do not have elasticity in all directions so as tobe able to conform to a compound curve. There are also available someheating devices which are made of an elastic material. In these elasticheating devices, the elastic insulating material is capable ofstretching or of elasticity in all directions. However, the heater wirepatterns of these elastic insulated heaters are so formed that they areincapable of stretching in more than one direction. Therefore, whilethese elastic insulated heating devices are capable of conforming tosimple curves they lack the necessary overall elasticity to conform tocompound curves. From the above it can be seen that there is presently aneed in the heating art for a simple and relatively inexpensive heatingdevice which will be able to readily conform to compound curves, withoutthe necessity of specifically designing or tailoring such heatingdevices to the exact curvature of the surfaces to which it is to beapplied.

It is, therefore, an object of this invention to provide a heatingdevice which will be elastic so as to stretch in all directions toreadily conform to a compound curvature of a surface to which it is tobe applied.

A further object of this invention is to provide a heating device havingthe necessary elasticity to be useful in installations having compoundcurvatures, the heating device having sufficient elasticity to readilymeet any changes in the designs of the compound curvature to 'which itis originally applied.

It is a further object of this invention to provide a simple andinexpensive heating device having high temperature capabilities andbeing provided with the necessary elasticity to readily conform to anycurvatures on the surface to which it is to be applied.

In carrying out this invention in one form a heating device is providedin which the pattern of the heater wire is so constructed and arrangedas to be stretchable in all on United States Patent 3,152,313 PatentedOct. 6, 1964 ice directions, the patterned heater wire being imbedded inan elastic insulation means having elasticity in all directions, tothereby enable the heater device to stretch in all directions so as toconform to any compound curves.

This invention, and the manner in which its objectives and advantagesare obtained will be better understood from the following descriptiontaken in connection with the accompanying drawing in which:

FIGURE 1 is a plan view of one form of a heater wire pattern which maybe utilized in the practice of this invention;

FIGURE 2 is a sectional view, taken on the line 2--2 of FIGURE 1, of aheating device formed in accordance with this invention; and

FIGURE 3 is a perspective view of a heating device, made in accordancewith this invention, as applied to a surface having a compoundcurvature, the heater wire pattern being shown in full lines.

Referring now to the drawing in which like numerals are used to indicatelike parts throughout, and in particular with reference to FIGURE 1,this invention is shown in a preferred form as a heating device 10 whichis comprised of an elastic insulation 12 and a patterned heater wire 14.As shown in FIGURE 1 the heating device 10 is in the form of a flat thinheater which may for example be applied to a metallic surface, such asfor example, by bonding, to apply heat to such surface. In thoseinstances in which the surface to which the heater device 10 is to beapplied contains a compound curve, it is desired that the heating device10 closely conform to such compound curve. In order that the heatingdevice 10 conform to such compound curve the wire carrying, electricalinsulation 12 is formed of an elastic material, such as for example, anatural or synthetic rubber. Where the heating device 10 is required togenerate very high temperatures for heating, the elastic material 12 mayfor example, be silicone rubber, which is well known for its ability towithstand high temperatures without deterioration. The heater wire 14,which is imbedded in the wire carrier 12, is patterned in a manner asshown in FIGURE 1 so as to provide the desired stretchability in alldirections. Present heating devices which are provided with an elasticinsulation are unable to conform to compound curves because the patternof the heater wire carried in such heating devices has elasticity ingenerally only one direction. To overcome this defect, the heater wire14 is patterned so that the runs 13 of the heater wire in the directionof the double headed arrow 16 are made in an undulated form so as to bestretchable, or have elasticity in the direction of the double headedarrow 16. The various connecting runs 15 in the direction of the doubleheaded arrow 18, which form the connection between the various runs inthe direction of the double headed arrow 16, are also patterned in anundulating form, so as to have a desired elasticity in the generaldirection of the double headed arrow 18. Thus, the heating device 10would have elasticity in all directions and therefore, would be able toclosely conform to any compound curvature on the surface to which it wasto be applied. While the runs 13 and 15 are shown as being substantiallyperpendicular to each other it will be understood that they maybepatterned in any desired configuration.

In constructing the heating device of this invention, a sheet or layerof elastic insulation, such as for example silicone rubber, is providedwith a number of pins or other means placed on the layer in the shape ofthe desired pattern. The heater wire 14 is then wound on these pins soas to assume the desired shape, such as for example, the pattern shownin FIGURE 1. A second layer of elastic insulation, for example siliconerubber, is then cemented to the first layer so as to form the desiredheating device and maintain the heater wire in its position between thetwo layers. When the layers have been cemented together the pins maythen be removed and the heater wire will be held in the desiredposition. Of course, in order to provide the desired current to theheater wire connections 202 are .provided at opposite ends of the heaterwire 14, as shown in FIGURE 1. An appropriate source of electricalcurrent may be attached to the connections 2tl2tl, for supplyingelectrical energy to the heating device ltl. The construction accordingto that set forth above is shown in FIGURE 2 where the heater wire 14 isshown as being firmly held in place between the elastic installation 12,which is formed of the layers 22 and 24- cemented together along theline 26.

Of course, it will be understood by those skilled in the art, that it isnot necessary that the elastic material be formed of two layers cementedtogether. For example, it is possible to suspend the heater wire at adesired height within a mold, and then to form a one piece elasticinsulation about the heater wire by filling the mold with the liquidform of an elastic insulation, and then setting or curing theinsulation. The heater wire could be suspended on rods or other deviceswithin the mold which could be removed after the curing of theinsulation, thereby giving a one piece construction which would besubstantially the same as the two layer construction, but would not beliable to any limitations which might be imposed by existing adhesivematerial.

FIGURE 3 shows the application of a heating device formed in accordancewith this invention to a compound curved surface, such as for example,the nose cone of a missile. In FIGURE 3 the heating device 10' iscomprised of an elastic insulating material 12, having imbedded thereina patterned heater wire 14. The heating element 10 is formed in a largesheet, such as that shown in FIGURE 1, and is then wrapped about theconical surface. As shown, the conical surface has a small end 28 and alarge end 36. In wrapping the heating device 10 about the conicalsurface one end of the heating device 11? is not required to stretch asit is wrapped around the smaller end 28, however, the end of the heatingdevice Til which is Wrapped around the end 30 is required to stretch aconsiderable amount. This stretching is indicated by the very smallamplitude of the undulations in the heater wire 14 at that end of theconical surface. Of course, it will be understood that if applied to aflat surface having a compound curvature therein, that the heatingdevice 10' would merely be required to stretch over the portion of thesurface composed of the compound curvature, thereby closely conformingto such compound curvature. It will be understood by those skilled inthe art that the pattern of the heater wire 14' may be in any desiredshape so long as it is enabled to stretch in all directions within theheating element. While there has been shown and described the presentpreferred embodiment of the invention, various modifications may be madeby those skilled in the art to which this pertains. Therefore, thespirit and scope of this invention including all such modifications isset forth in the appended claim.

What is claimed as new and which is desired to be secured by LettersPatent of the United States is:

A heating device capable of use in high temperature application andadapted to conform to compound curves comprising, a silicone rubberinsulation material, a heater wire embedded within said silicone rubberinsulation, said heater wire being formed in a pattern of a series ofundulations in one direction and a series of undulations in asubstantially perpendicular direction to said one direction, andconnector means connected to the ends of said heater wire and adapted toprovide electrical current to said heater wire.

References Cited in the file of this patent UNITED STATES PATENTS2,284,673 Munschak June 2, 1942 2,412,843 Spraragen Dec. 17, 19462,423,196 MacKendrick July 1, 1947 2,460,795 Warrick Feb. 1, 19492,584,302 Stein Feb. 5, 1952 2,631,219 Suchy Mar. 10, 1953 2,674,683Rand Apr. 6, 1954 2,718,584 Hariu Sept. 20, 1955

